1. Field of the Invention
The present invention is related to a liquid crystal display device and a related driving method, and more particularly, to a liquid crystal display device capable of increasing charge time and a related driving method.
2. Description of the Prior Art
Liquid crystal display (LCD) devices, characterized in low radiation, small size and low power consumption, have gradually replaced traditional cathode ray tube (CRT) devices and widely applied in electronic devices, such as notebook computers, personal digital assistants (PDAs), flat panel TVs or mobile phones.
In order to design an LCD device having low power consumption, it needs to be noted that panel loading and dynamic power consumption both increase with the panel size. Normally, the polarity of the voltages applied to the liquid crystal capacitors need to be inverted at a predetermined interval to avoid permanent damage caused by the polarization of liquid crystal material. Common driving methods includes dot inversion, line inversion and frame inversion. The LCD device has the heaviest loading when the polarity of the driving voltage begins to invert and the source driver is required to provide large amount of power to change the voltages of the data lines. Meanwhile, the charge time of the liquid crystal capacitors becomes shorter with the increase in operating frequency and panel resolution. If two driving voltages vary a lot, the ideal voltage level may not be obtained after polarity inversion due to insufficient charge time. Therefore, precharge is commonly employed for improving charge time.
Reference is made to FIG. 1 for a prior art LCD device 10. The LCD device 10 includes an LCD panel 12, a source driver 14, and two gate drivers 16 and 18. A plurality of parallel data lines DL1-DLm, a plurality of parallel gate lines GL1-GLn, and a plurality of display units P(1,1)-P(m,n) are disposed on the LCD panel 12. The data lines DL1-DLm and the gate lines GL1-GLn form a matrix, and the display units P(1,1)-P(m,n) are disposed on the locations where the corresponding data lines and the corresponding gate lines intersect. Each display unit disposed on the LCD panel 12 includes a TFT switch and a liquid crystal capacitor. Each liquid crystal capacitor is coupled to a corresponding data line via a corresponding TFT switch. The source driver 14 can generate data signals corresponding to display images, while the gate drivers 16 and 18 can generate gate signals for turning on the TFT switches. When the TFT switch of a display unit is turned on by a gate signal, the liquid crystal capacitor of the display unit can be electrically connected to a corresponding data line for receiving the data signal transmitted from the source driver 14. Based on the charges stored in the liquid crystal capacitors (the polarity of the stored charge is represented by “+” or “−”), the display units can display images of different gray scales by rotating liquid crystal molecules.
Reference is made to FIG. 2 for a timing diagram illustrating the operations of the prior art LCD device 10. In FIG. 2, the horizontal axis represents time and the vertical axis represents voltage level. CK_O, CKB_O and STV_O represent the clock signals and start pulse signals for operating the gate driver 16, while CK_E, CKB_E and STV_E represent the clock signals and start pulse signals for operating the gate driver 18. GS1-GS4 respectively represent the gate signals outputted to the gate lines GL1-GL4. DATA represents data signals, and DATA1-DATA4 respectively represent the data signals outputted to the same data line. T represents the operating period of the LCD device 10, A1-A4 represent normal charge periods, and P1-P4 represent precharge periods. When inputting the data signal DATA1, the gate signals GS1 and GS2 are both at high level, during which the pixel P(1,1) is in normal charge period and the pixel P(1,2) is in precharge period. In other words, the pixel P(1,2) is first precharged with the data signal DATA1 previously written into the pixel P(1,1). The correct data signal DATA2 is then written into the pixel P(1,2) during the subsequent normal charge period A2.
The prior art LCD device 10 can increase the charge time of the TFT switches (from T/4 to T/2) by precharging the display units. However, the effect of precharge is limited when the correct data signal of a data line differs a lot from the precharge data signal. Also, the LCD device 10 can provide line inversion or frame inversion, but is unable to achieve higher display quality of dot inversion.